Typical thin film read heads are located between shields. The shields improve head performance by shielding stray magnetic flux from the sensor element. Gap layers electrically insulate the shields from the sensor element and from abutting lead structures.
As read head structures become smaller to improve areal density, it is desirable to reduce the thickness of the insulative gap layers to optimize head sensitivity. Although reducing the thickness of the gap layers improves sensitivity by reducing the distance between the sensor and the shield, it also allows lead structures, deposited lateral to the sensor element, to more easily short to the shields. Such shorting can be due to flaws in, or degradation of, the gap material, or by defects created during the fabrication process. For example, a pinhole in the gap material can allow current to flow from a lead element to the shield.
Because shield-to-shield spacing is not as critical away from the sensor element, it is not necessary to have a thin gap in the areas away from the sensor element. As such, to reduce shorting, extra gap layers typically are deposited over the gap layers, at areas apart from the location of the sensor element. This increases the gap thicknesses in the regions about the sensor element, and as such, reduces the occurrence of shorting between the lead structures and the shields.
An example of such a structure is shown in FIG. 1. In this device the read head 10 has a shield 20 with extra gap layers 30 placed over the shield 20 and about a void 35. Placed over the extra gap layers 30 and the shield 20 is a first gap layer 40. Then, above the first gap 40 is a sensor layer 50, which includes leads 54. A cavity 60 is defined by the deformed shape of the sensor layer 50, caused by the void 35. Although the use of the extra gap layer 30 reduces shorting between the leads 54 and the shield 20, the present inventors have found such structures difficult to reliably manufacture with submicron track widths. Sub-micron track widths are necessary for high track density applications greater than about 15 Kilo tracks per inch and areal densities greater than about 7 Giga bits per square inch.
Because of the uneven surface created by laying the first gap layer 40 and sensor layer 50 over the void 35, and the relatively small width W of the cavity 60, variations in the track widths of the sensor element 52 of the sensor layer 50 tend to occur. These track width variations are due to the inherent variations in the width W and depth H of the cavity 60 and the effect the dip of the cavity 60 has on controlling the flow of the photoresist (which tends to pool in the cavity), used to etch the sensor layer 50 and define the track width of the sensor element. In addition, as the thickness of the photoresist is reduced to provide small structures, it is very difficult to adjust the thickness within the cavity 60.
Typically, photoresist thickness is controlled by spinning the workpiece to reduce the thickness of the photoresist. As the cavity 60 width and photoresist thickness is reduced, however, the surface tension of the photoresist causes a pool to form within the cavity 60. The pooling makes the photoresist resistive to change in its thickness. As such, it is very difficult to control photoresist uniformity across the workpiece and to control the thickness of any small photoresist structure formed within the cavity 60.
Because the track width of the sensor is directly related to the thickness of the photoresist used to define the sensor, the lack of photoresist uniformity causes a similar problem in controlling track widths. The resulting high variation in sensor track widths causes a significant number of devices to have track widths outside the manufacturing tolerances. Thus, the lack of photoresist uniformity caused by deposition over the cavity 60 results in a high rate of loss of devices during manufacture.
An another example of a sensor with increased gap thicknesses away from the sensor is the sensor disclosed in U.S. Pat. No. 5,568,335, by Fontana, et al., issued Oct. 22, 1996, entitled MULTI-LAYER GAP STRUCTURE FOR HIGH RESOLUTION MAGNETORESISTIVE READ HEAD, herein incorporated by reference in its entirety. In this device, the extra gap layer is deposited over the gap layer lateral to and away from the sensor element. It has been found that this type of structure is also difficult to reliably manufacture with submicron track widths. Therefore, such structures, while improving reliability of the read heads, prove to be an impediment to obtaining high areal density.
One approach to solve the problems associated with the use of extra gap material, involves etching the shield on either side of the sensor location to receive the deposition of the extra gap layer. This approach is advantageous as it avoids a deformed sensor layer by providing a relatively flat and smooth surface for the application of the sensor layer. An example of this approach is disclosed in U.S. patent application Ser No. 09/325,104 by Knapp, et al., Filed: Jun. 3, 1999, entitled DATA STORAGE AND RETRIEVAL APPARATUS WITH THIN FILM READ HEAD INSET EXTRA GAP INSULATION LAYER AND METHOD OF FABRICATION, herein incorporated by reference in its entirety. Although this approach significantly reduces the variations in track widths associated with the prior methods, some measure of sensor to shield shorting still may still occur. This shorting is typically due to the fencing of material at the edges of the extra gap layer. This fencing can cause shorts by providing connections between the shield and the sensor leads.
Therefore, a need exists for a narrow gap read sensor and method of fabrication thereof, which provides sufficiently small read track widths, with a minimum of width variation over a series of such sensors, and which sensor to shield shorting is significantly reduced or effectively eliminated.
The present invention provides a thin film read head, having a planar sensor element and an extra gap layer, and a method of fabrication thereof. The apparatus of the invention is a read sensor which includes a shield, a planar sensor element, a read gap positioned between the shield and the sensor element, and an extra gap positioned between the shield and the sensor element, and positioned adjacent the read gap. The sensor element is positioned in a sensor layer. With the sensor element and the shield separated by only the relatively thin gap layer, high sensitivity of the sensor element is obtained. Further, by placing the relatively thick extra gap between the shield and the sensor layer, and about the sensor element, the potential for shorting between the shield and the sensor layer is minimized. The shield can be planarized to provide a substantially planar read gap and sensor layer at, and about, the sensor element. This, in turn, results in improved control of sensor track widths by greatly reducing the potential for pooling of photoresist during fabrication of the read sensor.
By having the portion of the sensor layer containing the sensor element substantially planar, track width manufacturing variations are minimized. This is because the present invention eliminates the need to deform the sensor layer, as occurred in the prior art when the sensor layer had to be deposited over a cavity. That is, track width variations are reduced by positioning the sensor layer upon a substantially planar read gap layer. The read gap layer can be made substantially planar by laying it on a planarized upper surface of the shield.
The read gap is sufficiently wide to fully separate the sensor element from the shield. The read gap has edges on each of its sides. The extra gap is positioned generally adjacent to the read gap and the sensor element, and extends laterally therefrom. Preferably, the extra gap overlaps the edges of the read gap to assure electrical insulation between the sensor layer and the shield. In this manner, the sensitivity of the sensor element is maximized by placing only the relatively thin gap layer between the sensor element and the shield. At the same time, the potential for shorting between the sensor layer and the shield is minimized by placing the thicker extra gap between the sensor lead elements and the shield. The increased sensitivity of the present invention allows for use of media with areal density in the range of about 100 Gb/in2.
Preferably the extra gap and the read gap are alumina (Al2O3) and the shield is nickel iron (NiFe). Preferably, the read gap layer is between 200 xc3x85 and 400 xc3x85 thick.
In at least one embodiment, the invention includes a data storage and retrieval apparatus which includes a magnetic recording media, a head assembly located adjacent to the magnetic recording media, and a motor coupled to the media so as to move the media with respect to the head assembly. The head assembly in turn includes a write head and a read head. The read head includes a shield, a planar sensor element, a read gap positioned between the shield and the sensor element, and an extra gap positioned between the shield and the sensor element, and adjacent the read gap.
The method of the invention is for fabricating a read sensor and includes depositing a read gap onto a planarized shield, depositing an extra gap adjacent an exposed portion of the read gap, and depositing a sensor element onto the exposed portion of the read gap and adjacent the extra gap. The method can also include planarizing the upper surface of the shield to assure that the read gap, and thus the sensor element, are substantially planar. A chemical mechanical polish (CMP) is preferably used to planarize the shield. It is preferred that after depositing the read gap layer, portions of the read gap layer and shield are removed to define a read gap center portion having edges. Preferably, either ion milling or a reactive ion beam etch (RIBE) is used to remove these portions of the read gap and shield. The extra gap is then deposited over the exposed portions of the shield and preferably overlaying the edges of the read gap element.
In at least one embodiment of the method, the steps include planarizing a shield by chemical mechanical polishing, depositing a read gap layer onto the shield, removing portions of the read gap layer and portions of the shield about a read gap center element having sides (so that the shield has an exposed surface defined by the removed portion of the shield), depositing an extra gap adjacent to and contacting the read gap center element (where the extra gap is deposited over the exposed portion of the shield and over the sides of the read gap center element), depositing a sensor layer over the read gap center element and over the extra gap, and fabricating a read sensor within the sensor layer.